explicit basic_spanstream(std::span<charT> s,
ios_base::openmode which = ios_base::out | ios_bas::in);
basic_spanstream(basic_spanstream&& rhs);
void swap(basic_spanstream& rhs);
template<class charT, class traits>
void swap(basic_spanstream<charT, traits>& x, basic_spanstream<charT, traits>& y);
basic_spanbuf<charT, traits>* rdbuf() const noexcept;
std::span<charT> span() const noexcept;
void span(std::span<charT> s) noexcept;